The Cold Compost Pile
In many ways, this is the easiest way to build compost, and many people believe it's also the best. There's no fancy or expensive equipment to buy, no noisy chopping machine, no turning, and no worries about nitrogen/carbon ratios. This is probably the way compost was made for thousands of years.
The proponents of cold compost sometimes suggest that you should slow down a compost pile that's working too fast by adding soil to the mix. One reason for choosing a cold compost system over a hot one is to reduce the loss of nitrogen and carbon. The fast action of those microbes furiously eating away in a hot compost bin will literally burn away much of the carbon in the pile, and it releases ammonia into the air which reduces the fertilizing potential of the finished compost. A cold compost pile may have more plant nutrients when it's finished.
However, a cold compost pile can take two years or more to turn weeds and grass clippings into usable compost, and it must be kept well-covered to prevent the rain from leaching out the materials, and to keep the sun from drying it out.
One real benefit of a cold compost pile is the fact that you don't have to turn it - nature does its work, while you sit back and wait. If you leave the pile to cure for two years, most weed seeds should be dead, and any plant diseases that were added to the pile should also be consumed and neutralized by the microbes in the pile.
The Hot Compost Pile
To make a hot compost pile you put layered materials onto a pile at least 3 feet high, then turn it regularly to get oxygen to the bacteria doing the work.
When you can get a compost pile like this to work the way it's supposed to, it gets hot enough to kill almost all the weed seeds in the pile. It should also kill any bad bacteria that might be attached to the material that goes into the compost. Getting the pile hot enough to kill seeds and bacteria is an art in itself. The best way to get a compost pile hot fast is to use plenty of manure and bedding from a local stable or cow barn, and chop your green material as small as possible. If you don't have any manure, getting a pile truly hot is very difficult, and no amount of turning will make it hot if there isn't enough nitrogen in the pile.
If you put straw in the pile along with the manure you may not need to turn the compost, since the straw will provide enough space for air. Most people who are true aficionados of hot compost insist on turning the pile as often as possible, because this will flood the pile with oxygen and restart the heat-loving bacteria.
The primary benefits of hot compost are the shorter amount of time it takes to reduce kitchen scraps and weeds into usable compost, and the fact that seeds and bad bacteria should be killed if the pile got hot enough. The primary benefits of cold compost is the reduction of work (no turning) and more plant nutrients for the garden. Which system is "better" will be debated by serious gardeners for years to come.
